As cities expand with multiple centres spread over massive regional hinterlands, the need to better understand the geographical variation across and within cities has become more pressing. This need applies strongly to issues of travel sustainability, where urban centres differ greatly in the accessibility they facilitate for private, public and active transport.
Spatial indicators are a useful tool to summarise complicated intrametropolitan patterns, as illustrated in my new working paper mapping CO2 emissions from journey-to-work travel across the London Region. The results of this indicator show a massive range of travel emissions by workplace of up to 300%, with particular problems for airports and the specialised employment region of the Western Sector, as can be seen in the map above.
This paper was co-authored with Joan Serras at CASA, who helped with the development of the road and public transport network analysis to model realistic routing behaviour from origin and destination flows from the 2001 census. One interesting aspect to this was the inclusion of GPS data to model average road speeds in London as illustrated below:
Full paper abstract:
“This paper develops a methodology for estimating network distances and CO2 emissions for UK census ward-level journey-to-work interactions. Improvements are made on existing empirical measures by providing comprehensive intra-metropolitan analysis; increasing network routing accuracy with UK public transport timetable and GPS-based average road speed data; allowing multimodal travel; and developing metrics suitable for travel sustainability analysis. The output unit of CO2 emissions has been selected to enable the integration of mode-choice and travel distance data, and to aid compatibility with integrated assessment applications.
The methodology is applied to the case study of the London Region for the year 2001. A very high degree of intra-metropolitan variation is identified in the results. Employment sub-centres diverge in their per-capita CO2 emissions by up to 300%, with specific problems of carbon intensive commuting to major airports and the specialised employment region of the Western Sector. These findings indicate that subcentre travel variation may be intrinsic to polycentric urban structures. The paper discusses means to improve the methodology, in relation to issues of coefficient disaggregation and modelling more complicated multi-modal trips.”